Desmoplastic fibroma

Desmoplastic fibroma of bone is a rare, locally aggressive, nonmetastasizing neoplasm of fibroblastic origin, classified by the WHO (2022) as an intermediate (locally aggressive) bone tumor analogous to soft tissue desmoid-type fibromatosis.[1][2] It accounts for approximately 0.1%–0.3% of all primary bone tumors.[3] In the jaws, the posterior mandible is the predominant site.[1] The pathogenesis remains incompletely understood; CTNNB1 mutations—common in soft tissue desmoid tumors—have been documented in only a few gnathic cases, and their role is considered controversial.[1][4] Radiographically, desmoplastic fibroma typically presents as a well-defined, radiolucent, expansile lesion with internal pseudotrabeculation.[5] Definitive management is surgical, with resection preferred to minimize recurrence.[1][6]

• Current WHO designation (2022): Desmoplastic fibroma of bone, classified under intermediate (locally aggressive) fibrogenic tumors.[1][2]
• Accepted synonym: Desmoplastic fibroma of bone (DFB); when specifically involving the jaws, "desmoplastic fibroma of the gnathic bones" (DFGB) is used in the literature.[1]
• Relationship to soft tissue counterpart: Considered the intraosseous analogue of desmoid-type fibromatosis (aggressive fibromatosis). The two entities share histologic features but differ in site of origin and some molecular characteristics.[1][3][4][7]
• Obsolete or confusing terms: Should not be confused with desmoplastic ameloblastoma, a histologic variant of ameloblastoma with a desmoplastic stroma but of odontogenic epithelial origin.[8][9]

• Frequency: Extremely rare; represents [3][10]
• Age: In the gnathic bones, the mean age is approximately 18 years, with the first decade of life most commonly affected (40.6% of jaw cases). Across all skeletal sites, the mean age is higher (~23–25 years), with approximately 74% of patients in the first three decades.[1][7][11]
• Sex: No consistent sex predilection. A slight female predominance (55.8%) has been reported in gnathic cases, while some skeletal series show equal distribution or slight male predominance.[1][6][7][11]
• Anatomic distribution:
  • Among all bones, the mandible, femur, and pelvis are the most frequent sites.[5][6]
  • Within the jaws, the mandible accounts for approximately 81% of cases, with a predilection for the posterior body and ramus.[1]
  • Maxillary involvement is uncommon (~19% of jaw cases).[1][10]

Presentation and symptoms

• The most common presentation is a painless, slow-growing swelling (54% of gnathic cases).[1]
• Facial asymmetry is the second most frequent finding (~33%).[1]
• Approximately 82% of gnathic cases are painless; pain is reported in a minority (~18%).[1]
• Mean evolution time before diagnosis is approximately 8 months, though some lesions are present for years before detection.[1]

Additional findings

• Tooth involvement—including mobility and toothache—is reported in approximately 10% of jaw cases.[1]
• Trismus or limitation of mouth opening occurs occasionally.[1]
• Pathologic fracture is uncommon in the jaws but is reported in approximately 12% of all skeletal desmoplastic fibromas.[11]

Tempo and red flags

Growth is characteristically slow but relentless, with progressive bone destruction. Rapid enlargement, pain, or paresthesia should raise concern for a more aggressive process and prompt expedited biopsy.[1][11]

Location and distribution

• The posterior mandibular body and ramus are the most common jaw sites.[1]
• Maxillary lesions are less frequent and may extend into the maxillary sinus or orbital floor.[10][12]
• Lesions are centered within the medullary cavity and expand outward.[5][13]

Periphery and shape

• Well-defined margins are present in approximately 65% of gnathic cases; the remainder show poorly defined or indistinct borders.[1]
• The zone of transition is characteristically narrow, and margins are typically nonsclerotic.[5]
• Shape ranges from round or ovoid in smaller lesions to irregular and lobulated in larger tumors.[10]

Internal architecture

• The internal pattern is radiolucent/hypodense in approximately 84% of cases.[1]
• A multilocular appearance is slightly more common than unilocular (approximately 57% vs. 43% among cases where locularity was specified).[1]
• Internal pseudotrabeculation—coarse, irregular bony septa traversing the lesion—is a hallmark feature, reported in 91% of cases in the largest radiographic analysis. These septa are irregular in thickness and orientation, producing a honeycombed or compartmentalized appearance that may help distinguish desmoplastic fibroma from odontogenic cysts.[1][5]
• A minority of cases (~14%) show a mixed radiolucent-radiopaque pattern; purely radiopaque lesions are exceedingly rare (~2%).[1]

Effects on teeth and adjacent structures

• Tooth displacement is common, reported in approximately 32% of gnathic cases.[1]
• Root resorption is less frequent (~13%), which is a useful observation because many odontogenic tumors (e.g., ameloblastoma) cause more prominent resorption.[1]
• Tooth mobility may be present when the lesion undermines the alveolar process.[1]

Growth pattern and cortical involvement

• Bone expansion is a near-universal feature, present in approximately 95% of gnathic cases.[1]
• Expansion occurs through gradual periosteal apposition of new bone on the outer cortex, producing widening of the host bone. However, distinct periosteal new bone formation (e.g., lamellated or spiculated reaction) is rare, occurring in only ~2% of intraosseous cases and ~9% of gnathic cases.[1][5]
• Cortical thinning, perforation, or destruction is reported in approximately 28%–45% of cases.[1][5]
• Soft tissue extension occurs in roughly 35% of gnathic cases and up to 48% across all skeletal sites, reflecting the locally infiltrative nature of the tumor.[1][11]

Recognized variants

• Rare periosteal (juxtacortical) desmoplastic fibromas have been described, presenting as surface-based lesions with cortical erosion and soft tissue mass rather than the typical intramedullary expansile pattern.[5]

MRI characteristics

• On T1-weighted images, desmoplastic fibroma shows low to intermediate signal intensity, similar to skeletal muscle.[14][15]
• On T2-weighted images, the lesion displays heterogeneous signal with areas of intermediate to high intensity interspersed with foci of low signal intensity. These low-T2 foci correspond to dense collagenous stroma rather than calcification and are a relatively distinctive feature that should raise consideration of desmoplastic fibroma among fibroosseous lesions.[14][15][16]
• Gadolinium enhancement is inhomogeneous.[14]
• Cystic changes have been reported in a minority of cases (~38% in one small series), which may cause confusion with malignant lesions.[17]
• MRI is superior to CT for delineating intramedullary extent, soft tissue extension, and the relationship to neurovascular structures, making it the preferred modality for preoperative surgical planning.[11][14][18]

CT characteristics

• CT demonstrates a hypodense, expansile, osteolytic lesion with internal septations corresponding to the pseudotrabeculation seen on radiographs.[1][14]
• CT provides more accurate assessment of cortical integrity, including breakthrough and the extent of cortical thinning, compared with conventional radiography.[14]

Desmoplastic fibroma of the jaws produces a nonspecific radiolucent, expansile, often multilocular appearance that overlaps with a broad range of odontogenic and nonodontogenic lesions. The combination of internal pseudotrabeculation with irregular septa, marked expansion, relatively infrequent root resorption, and absence of internal mineralization narrows the differential, but biopsy remains essential for definitive diagnosis.[1][5][19]

The highest-risk diagnostic pitfall is misdiagnosis as a low-grade fibrosarcoma, which shares overlapping histologic features. Absence of mitotic activity, nuclear atypia, and necrosis favors desmoplastic fibroma, but incisional biopsy with adequate tissue sampling is mandatory to exclude malignancy.[1][3][13]

Microscopic features

• The tumor is composed of slender, spindle-shaped fibroblasts with elongated, wavy nuclei arranged in loose fascicles or bundles within an abundant collagenous stroma.[1][7][13]
• Myxoid areas are present in approximately 38% and hyalinized zones in approximately 28% of gnathic cases.[1]
• Mitotic figures are absent or exceedingly rare; nuclear pleomorphism, atypical mitoses, and necrosis are not features of this tumor.[1][13]
• Low cellularity and bland cytology distinguish desmoplastic fibroma from low-grade fibrosarcoma, the most important histopathologic mimic.[1][3][13]

Immunohistochemistry

• Vimentin is consistently positive.[1]
• Smooth muscle actin (SMA) is positive in approximately two-thirds of tested cases.[1]
• β-catenin nuclear positivity is present in roughly 66% of tested cases and, when present, supports the diagnosis and the relationship to desmoid-type fibromatosis.[1][4]
• S-100 protein is characteristically negative, helping exclude neural tumors.[1]
• Ki-67 proliferation index is low (mean ~1.5%), which aids in excluding malignant spindle cell neoplasms.[1]

Radiologic-pathologic correlation

The coarse pseudotrabeculation seen radiographically corresponds to residual bony septa entrapped within the expanding fibrous tumor mass. The predominantly radiolucent character reflects the nonmineralized collagenous and myxoid stroma.[5][13] The rare mixed or radiopaque appearance may correspond to areas of hyalinization or reactive bone at the tumor periphery.[1]

Workup and referral

• Incisional biopsy is required for definitive diagnosis, as imaging features are nonspecific.[1][19]
• Cross-sectional imaging (preferably MRI) should be obtained preoperatively to define the full extent of intraosseous and extraosseous disease and the relationship to vital structures.[11][14]

Surgical treatment

• Resection (segmental or marginal) is the preferred treatment and is associated with the lowest recurrence rates.[1][6][11]
  • In the gnathic bones, segmental resection with immediate reconstruction (e.g., fibula free flap, rib graft) is the standard approach, particularly in pediatric patients to preserve craniofacial development.[23][24][25]
• Curettage (with or without adjuvants) carries a substantially higher recurrence rate (55%–72% across all skeletal sites vs. ~17% after resection). In the jaws, curettage may be considered for small, well-contained lesions when resection would cause disproportionate morbidity, with the understanding that close surveillance is essential.[6][11][13]

Recurrence and prognosis

• Overall recurrence in gnathic cases is approximately 10.8%, with all recurrences reported in the posterior mandible.[1]
• Across all skeletal sites, recurrence rates are higher (23% overall; up to 55%–72% after curettage alone).[6][11]
• No recurrences have been reported after resection with wide surgical margins.[11]
• Metastasis is not a recognized feature of desmoplastic fibroma; rare reports of metastasis after multiple recurrences are exceptional and disputed.[11][13]
• Long-term clinical and radiographic surveillance is recommended, as recurrences may develop years after initial treatment.[6][26]

Syndromic associations

• Familial adenomatous polyposis (FAP): Desmoplastic fibroma of the jaw may be an early extracolonic manifestation of FAP. Genetic screening for APC mutations should be considered when desmoplastic fibroma is diagnosed, particularly in young patients.[1][23]
• Tuberous sclerosis complex: An association has been reported in a small number of cases (4 of 96 in one systematic review), warranting clinical awareness.[1]

Pediatric considerations

Desmoplastic fibroma disproportionately affects children and adolescents. In pediatric jaw cases, immediate reconstruction after resection is important to support ongoing craniofacial growth.[24][25] Rib grafts and vascularized fibula flaps have both been used successfully in this population.[23][25]